A semiconductor device used for a central processing unit (CPU) or the like is electrically connected to and fixed on a board. The temperature of the semiconductor device becomes so high at the time of its operation that the semiconductor device cannot function well unless its temperature is forcibly reduced.
Accordingly, a heat radiation component such as a heat spreader or a radiator fin (or a heat pipe) is attached on the semiconductor device to ensure a path for effectively radiating heat generated by the semiconductor device to its outside. Attempts have been made at smooth heat conduction by interposing a thermal interface material (TIM) between the semiconductor device and the heat radiation component such as a heat spreader so that the thermal interface material follows their respective uneven surfaces to reduce thermal contact resistance.
FIG. 1 is a cross-sectional view of a semiconductor package including a conventional heat radiation component. Referring to FIG. 1, a semiconductor package 100 includes a board 200 and a semiconductor device 400 mounted on the board 200 via connection terminals 300. The space between the board 200 and the semiconductor device 400 is filled with underfill resin 500.
A heat radiation component 700 on which a metal layer 750 is formed is attached on the semiconductor device 400. A thermal interface material 600 is interposed between the semiconductor 400 and the metal layer 750. The heat radiation component 700 is fixed to the board 200 with an adhesive agent 800.
In the semiconductor package 100, heat generated by the semiconductor device 400 mounted on the board 200 is transferred to the heat radiation component 700 via the thermal interface material 600 provided on the semiconductor device 400. Thus, the thermal interface material 600 is used as a part configured to thermally connect the semiconductor device 400 and the heat radiation component 700 without their direct contact.
Examples of the material of the thermal interface material 600 include indium, which has good thermal conductivity. For example, in the case of using indium as the material of the thermal interface material 600, the semiconductor package 100 is heated to, for example, approximately 180° C. in order to melt the thermal interface material 600 formed of indium, and is thereafter returned to normal temperature at the time of attaching the heat radiation component 700 onto the semiconductor device 400 through the thermal interface material 600.
Here, for example, the semiconductor device 400 has a coefficient of thermal expansion of approximately 3 ppm/° C. if the semiconductor device 400 is made of silicon, and the board 200 has a coefficient of thermal expansion of approximately 15 ppm/° C. if the board 200 is based on an FR-4 board (a copper-clad laminate having a flame-resistant glass cloth base material impregnated with epoxy resin). Heating the semiconductor package 100 and thereafter returning the semiconductor package 100 to normal temperature as described above results in warpage of the semiconductor package 100 due to the difference in the coefficient of thermal expansion between the semiconductor device 400 and the board 200.
For related art, reference may be made to, for example, Japanese Laid-open Patent Publication No. 4-186869 and Japanese Laid-open Patent Publication No. 2004-327711.